Shell has pulled back from its renewable investments, claiming they are 'not economic' Photograph: James Boardman/Public Domain

Shell, I have to report, is the new Exxon. The company that back in December was filling this and other newspapers with double-page adverts promoting its conversion to a "new energy future" of wind farms, hydrogen fuels, fuel made from marine algae and much else, has pulled the plug.

In the 1990s Royal Dutch Shell set its boffins on finding new green fuels, such as forest plantations to make biofuels. I remember them at the Earth Summit in Rio back in 1992. Not long after, Shell was for a time the world's second largest manufacturer of solar panels. In 2004, it opened the world's largest grid-connected solar park.

The company seemed to embrace the idea that a modern global oil company could and should transform itself into a green energy company. But, to rewrite its old advertising slogan, you can never be sure of Shell.

In recent years, Shell has invested more than $1bn in the most commercial of the new renewable industries, wind power. It claims to have more than 500MW of wind power capacity altogether — the equivalent of half a regular power station.

The company claimed at the time that it was going to concentrate its renewables business in the US. Now that promise has quietly disappeared. Last week, its head of gas and power, Linda Cook, told reporters: "We do not expect material amounts of investment [in wind and solar] going forward." Biofuels will still get cash. Everything else is back into cold storage.

Why? "They continue to struggle to compete with other investment opportunities we have in our portfolio." In other words, oil prices are back down and Shell is in this for the short term.

We are left with those, shall we say unfulfilled, ads. "Tackling climate change and providing fuel for a growing population seems like an impossible problem, but at Shell we try to think creatively," said one. If you keep old newspapers, you'll find it across the centrefold of the Guardian on 15 December. If not, a version is still on their web site.

But now we know the creative thinking had more to do with advertisement copywriting rather than energy technology.

The ad continues: "It won't be easy. Innovative solutions rarely are. But when the challenge is hardest, when everyone else is shaking their heads, we believe there is a way." Do smile, amid your tears.

Clearly it hasn't been chastened. Those pre-Christmas ads were more greenwash. But, for anyone who has watched the company over the years, what has happened is not so much a cynical misrepresentation of its policies as an outright betrayal of past promises.

In the race for a greener future, Shell could have been a contender. Now it is on the canvas, flat out cold.

• How many more green scams, cons and generous slices of wishful thinking are out there? Please email your examples of greenwash to greenwash@theguardian.com or add your comments below